1. Field of the Invention
This invention generally relates to the field of manufacture of porous metal structures.
The invention is more particularly directed to the field of manufacture of porous metal structures for the purpose of applications such as supports for electrodes, catalysts, filters, sound insulators or the like.
2. Description of the Prior Art
Methods have already been proposed for the manufacture of metallic structures having a cellular or fibrous character and employed in the electrochemical industry.
The structures considered are of the porous or highly porous type and are provided in the form of a three-dimensional lattice network which defines a plurality of spaces in communication with each other.
These porous supports which it is desired to metallize or put in a conductive state are often fabricated from a synthetic or artificial porous material which is then made conductive, for example by means of a chemical surface treatment.
In consequence, the initial structure is constituted by said porous support, which can be an agglomerate of fibers whether in an ordered state or not and consisting, for example, of a felt, a woven fabric or a reticulated structure.
When a reticulated structure is employed, and in order to obtain at the outset an open-pore structure or in other words a structure in which the cells can communicate with each other, a processing step known as "uncapping" is performed with sodium hydroxide, for example.
The structure thus obtained can then be coated, for example, with a conductive or partially conductive material by chemical or electrochemical process. Methods have thus been proposed for depositing a metal by reduction of ammoniacal silver nitrate in situ.
After this step, provision can be made in certain cases for a second metal coating deposited by chemical and/or electrochemical process. On completion of these two steps, the initial support can then be removed and the metal may be annealed if necessary.
It has been generally considered that these methods could give rise to major practical difficulties at the industrial development stage.
These difficulties are essentially related to the complexity of the operating cycles which are involved and to the large number of liquid-phase treatments carried out successively (processing steps which involve uncapping, sensitization, chemical and electrochemical metallizations), thus entailing the risk of pollution of baths with respect to each other and defects of reproducibility.
For further details, reference can be made to French patent application No. FR 70 22469 filed on June 18th, 1970. Those versed in the art can also refer to French patent application No. FR 79 17540 assigned to the same assignee as the present application and relating to electrode supports and their applications for electrochemical generators. This specification describes a method for obtaining structures of the same category as those of the present invention and their applications.
The methods described in said French patent application No. FR 79 17540 prove satisfactory in regard to the results achieved but do not remove the disadvantages which have already been mentioned and which arise at the industrial development stage except in the event of particularly stringent inspection testing.
Finally, from a general standpoint, it is always desirable to endeavor to reduce the costs of existing methods and to make them even easier to carry into practical effect; these are two of the advantages obtained by means of the present invention.